The simple answer is yes. You have 2 options;
1 Create the rounded edge in the mould
2 Round the edges of the concrete once its been cast by hand-sanding or routing the edges with a diamond brazed profiling cutter (see image below)
For option 1 how you build the mould will depend on whether you are casting insitu or prefabricating your concrete.
For prefabrication, using silicone sealant and common silicone shaping tools is the best option.
For Cast-In-Place a more complex solution is required and may involve using mini-guttering for example to create a bullnose. This does depend on your specification and also how flexible you are in your design so that you can marry up your finish with the materials and products you can source to make your mould.